1. Field of the Invention
The invention generally relates to a method and device for extracting kinetic energy from a stream of fluid containing a mixture of liquid and vapor, herein referred to as a two-phase fluid, and more particularly to an improved method and turbine particularly suited for use in separately extracting kinetic energy from each phase of a two-phase fluid which tends to characterize geothermal sources of power.
2. Description of the Prior Art
The prior art is, of course, replete with turbines adapted for use in extracting kinetic energy from streams of fluids such as water in its liquid phase, and/or in its vapor phase.
As can readily be appreciated by those familiar with the design and operation of turbines, such as stream turbines and the like, the use of two-phase fluids is severely impaired in instances where the fluid is delivered to a turbine in both its liquid and vapor phase, since the velocity of the vapor tends to exceed the velocity of the liquid resulting in reduced efficiency. Consequently, various attempts have been made to separate the liquid phase from the vapor phase of a fluid, prior to the delivery of the fluid to a turbine, employing systems which permit the vapor phase, or steam, to drive a turbine while the liquid phase of the fluid is discharged as waste.
With the advent of an increased interest in the development of sources of geothermal power, increased attention is being given to the development of turbines capable of utilizing two-phase fluids such as mixtures of vapor and liquid. In order to achieve a maximum output from such a turbine, it is apparent that kinetic energy must be extracted from both the liquid phase and the vapor phase of the given fluid. Finally, it has long been recognized that small, closed-cycle engines using steam can be operated at lower, more desirable shaft speeds, and achieve certain other advantages upon a mixing of an inert liquid with steam provided as the primary source of energy.
Conventional turbines, such as impulse turbines, are not totally suitable for use in extracting energy for two-phase fluids because of the inherent tendency of the liquid phase to separate from the vapor phase and follow a path of its own. Attempts have been made to solve the problems which attend the existence of separate flow paths for liquid and vapor phases of a fluid delivered to a turbine. These attempts have resulted in systems such as the system disclosed in U.S. Pat. No. 3,879,949. However, turbines of this type tend to be complex, excessively bulky and costly, particularly where such a turbine is designed to be employed for extracting kinetic energy from a flow of a two-phase fluid derived from a geothermal source.
It is, therefore, the general purpose of the invention to provide a simple, economic and practical turbine particularly suited for use in extracting kinetic energy from a stream of two-phase fluids, such as a stream of fluid containing both steam and water, which overcomes the aforementioned difficulties and disadvantages without sacrificing the recognized advantages previously attributable to turbines in extracting kinetic energy from streams of fluid.